Mechanisms of sod2 gene amplification in Schizosaccharomyces pombe
Mechanisms of sod2 gene amplification in Schizosaccharomyces pombe
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DOI：
10.1091/mbc.11.3.873
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发表时间：
2000-03-01
影响因子：
3.3
通讯作者：
Patterson, TE
中科院分区：
文献类型：
--
作者：
Albrecht, EB;Hunyady, AB;Patterson, TE
真核生物中的基因扩增在耐药性、肿瘤发生和进化中起着重要作用。粟酒裂殖酵母sod 2基因提供了一个有用的模型系统来分析这一过程。sod 2位于染色体I的端粒附近，编码质膜Na+（Li+）/H+反向转运蛋白。sod 2扩增后，S.粟酒裂殖酵母在其它致死浓度的LiCl中存活，并且>90%的扩增的sod 2基因发现于180-和225-kb的线性扩增子中。180-kb扩增子的新接头的序列表明，它是通过染色体I的长臂和染色体II的短臂的端粒附近的同源区域之间的重组形成的。225-kb扩增子的分离频率是180-kb扩增子的三倍，是来自染色体I端粒附近区域的回文序列。该回文的对称中心包含由290个碱基对间隔区分隔的两个相同的134个碱基对序列组成的反向重复序列。LiCl抗性突变体在拓扑异构酶或DNA连接酶活性缺陷的菌株中比在野生型菌株中出现的频率高200-600倍，但突变体细胞含有相同的扩增子。这些数据表明，扩增子的形成可能开始与DNA损伤，如断裂。在225-kb扩增子的情况下，断裂可导致发夹结构，其然后被复制以形成双链线性扩增子，或导致十字形结构，其然后被解析以产生相同的扩增子。
Gene amplification in eukaryotes plays an important role in drug resistance, tumorigenesis, and evolution. The Schizosaccharomyces pombe sod2 gene provides a useful model system to analyze this process. sod2 is near the telomere of chromosome I and encodes a plasma membrane Na+(Li+)/H+ antiporter. When sod2 is amplified, S. pombe survives otherwise lethal concentrations of LiCl, and >90% of the amplified sod2 genes are found in 180- and 225-kilobase (kb) linear amplicons. The sequence of the novel joint of the 180-kb amplicon indicates that it is formed by recombination between homologous regions near the telomeres of the long arm of chromosome I and the short arm of chromosome II. The 225-kb amplicon, isolated three times more frequently than the 180-kb amplicon, is a palindrome derived from a region near the telomere of chromosome I. The center of symmetry of this palindrome contains an inverted repeat consisting of two identical 134-base pair sequences separated by a 290-base pair spacer. LiCl-resistant mutants arise 200-600 times more frequently in strains deficient for topoisomerases or DNA ligase activity than in wild-type strains, but the mutant cells contain the same amplicons. These data suggest that amplicon formation may begin with DNA lesions such as breaks. In the case of the 225-kb amplicon, the breaks may lead to a hairpin structure, which is then replicated to form a double-stranded linear amplicon, or to a cruciform structure, which is then resolved to yield the same amplicon.